Aluminum base alloy for die castings



3,019,101 ALUMINUM BASE ALLOY FGR DRE CASTINGS Donald L. Colwell, ShakerHeights, Ohio, assignor to Apex Smelting Company, Chicago, Ill., acorporation of Illinois No Drawing. Filed Apr. 28, 1960, Ser. No. 25,21515 Qlaims. (Cl. 75-141) This invention relates to aluminum base alloysand more particularly to alloys of this nature, suitable for diecasting, and adapted to exhibit a pleasing finish when an anodic coatingis applied thereto. This application is a continuation-in-part of myco-pending application, Serial No; 762,213, filed September 22, 1958,now abandoned, for Aluminum Base Alloy for Die Castings.

As is well known to those skilled in the art of die casting aluminumbase alloys, as an alloy approaches closer and closer to the compositionof pure aluminum, it becomes more and more difiicult to produceacceptable die castings therefrom. The lower the alloy content in thealuminum, the higher is the melting point of the heat of metal, and ofcourse the metal must be introduced into the die at a temperaturesufiiciently above its melting point so that it will fill theinterstices of the casting cavity before the metal begins to solidify.On the other hand, a high alloy content of the alloying ingredientsinduces a lower melting point, so that the metal, the dies, and thevarious items of casting equipment, can be run at a substantially lowertemperature.

When die casting is attempted at the higher temperatures, because oflower alloy content in the melt, certain disadvantages are encountered,principally'the sluggishness of the metal and its tendency to adhere tothe die surface constituting the casting cavity walls. Since, for apurpose to be hereinafter explained, it is desirable that certain metalparts be die cast from low alloy stock, those working in the art haveexpended considerable eiiorts to avoid this soldering" or welding effectby applying various coatings to the casting cavity wall, but thesecoatings wear away rapidly, and it is usually quite impracticable toattempt to maintain such coating. Such procedure also disturbs thethermal equilibrium so desirable in a continuous die casting processwherein castings are made and ejected in uniform short cycle succession,every few seconds. It might therefore be concluded that the easiest wayto run a successful die casting process is to load the alloy with someof the usual alloying ingredients which are known to afford good castingproperties with adequate mechanical and physical properties.

There is however a large demand for die cast aluminum items which willpresent a pleasing finish as to texture, grain, and color when subjectedto any suitable oxide coating process, such as those coatings which canbe applied chemically or electro-chemically by various etching agents.Merely as an example I may mention the class of hardware includingautomobile door and window operatin g handles, control knobs, trimitems, escutcheon plates, drawer pulls, etc. More and more these andsimilar items are beginning to illustrate the fact that eye appeal isone of the best sales arguments, and the female taste on a relativelyinexpensive portion of the complete article may determine whether or nota sale is made.

It is therefore desirable, iirst that these articles be made as diecastings, if their contour permits easy ejection from the die, becausedie casting becomes economically feasible when thousands of articles areto be produced. It is also desirable that the die cast article accept apleasing oxide finish, either of the whitish satin type, or one of themany color tinted coatings now available, principally by anodicprocesses.

Unfortunately the manufacturer has heretofore been fires int confrontedby a dilemma which is this: if the article has a low alloy content,approaching commercial aluminum ingot, it will yield an excellent oxidecoated finish, either plain or in color, but for reasons hereinabovenoted it will not be an easy or profitable die-casting job. If on theother hand the composition be changed to an aluminum alloy base with asubstantial content of alloying ingredients which make for good diecasting properties the cast article will not take a good oxide coating.It will be of uneven finish and texture, and colored coatings will bedull and nonuniform.

An object of the present invention is to provide an aluminum base alloyhaving excellent die casting properties which nevertheless yields a mostpleasing oxide-coated finish.

A further object of the invention is to provide an aluminum base alloyas defined in the last preceding paragraph which contains alloyingingredients eifective to give adequate physical properties either in theas-cast or heat-treated condition.

A further object of the invention is to provide an aluminum base alloyas defined in the two immediately preceding paragraphs, and containingspecifically limited amounts of Zinc, antimony, and iron, with possiblespecifically limited amounts of magnesium, manganese, silicon. andcopper.

Other objects and advantages of the invention will appear as thefollowing description proceeds.

The principal alloying ingredient of my alloy is Zinc which should bepresent in the alloy in an amount between 3.5 percent and 6.0 percent.The alloy also contains between about 0.6 percent and 2.0 percent oftotal iron, which includes any iron present inadvertently as animpurity. The alloy further contains between 0.25 percent and 2.0percent of antimony.

As a preferred composition within the above range I suggest thefollowing: 4.5 percent of zinc, 0.9 percent of iron, and 1.0 percent ofantimony, the balance being substantially aluminum with the usualimpurities.

Alloys within the range indicated, and especially of the preferredcomposition, can be die cast without any difiiculty and exhibit asurface, when oxide-coated, equal to the best surface heretoforeavailable even with relatively pure aluminum unalloyed ingot. An alloyof the preferred composition, in the cast condition, has, on theaverage, a tensile strength of twenty eight thousand pounds per squareinch, 2. yield strength of twenty thousand pounds per square inch, andabout twelve percent elongation. These properties may be varied bysuitable thermal treatments, as will be understood by those skilled inthe process of heat treating aluminum base alloys. I have discoveredthat the addition of antimony not only contributes to a very pleasingoxide-coated finish, but also materially reduces the tendency of thealloy to weld or stick to the die.

I have further discovered that the casting properties of the alloysdescribed hereinabove may be improved Without harmful deterioration ofthe coating characteristics by the addition of 0.15 to 0.5 percent ofmanganese, 0.15 to 0.5 percent of magnesium, and/or up to 2.0 percent ofsilicon, and/ or 0.1 to 2.0 percent of copper. The lower limit of thesilicon has not been specifically defined since silicon is present as animpurity in all commercial aluminum base alloys. Silicon will improvethe casting characteristics considerably, but, when used with the basealloy in the amounts noted, causes only slight deterioration in theoxide-coated finish, and this is permissable for certain adaptations incases where die configurations may demand exceptional castingcharacteristics, and a slight variation in coated appearance is notobjectionable. The magnesium, silicon and copper within the noted rangemay be used singly or in any suitable combination. The silicon is mosthelpful in improving casting characteristics, with copper and magnesiumfollowing in the order herein noted. The manganese assists thenon-sticking characteristics of the alloy, and the copper hardens andstrengthens the alloy.

Coating methods form no part of the present invention but it may bementioned here that suitable frosted-finished coatings are achieved, forexample, by a chemical dip in alkaline or acid reagents, which mayproduce a colored etfect by the inclusion of suitable dyes. Anodiccoatings are formed electrochemically, and may be produced in anextensive variety of colors by the use of dyes. The alloys hereindisclosed and claimed lend themselves readily both to the chemical andelectrochemical methods of coating.

What is claimed is:

1. An aluminum base alloy suitable for die castings, and consistingessentially of between 3.5 percent and 6.0 percent of zinc, between 0.6percent and 2.0 percent of iron, and between 0.25 percent and 2.0percent of antimony, the balance being substantially all aluminum, andcharacterized by an adaptability to acquire an excellent finish whenoxide coated.

2. An aluminum base alloy suitable for die castings, and consistingessentially of about 4.5 percent of zinc, about 0.9 percent of iron, andabout 1.0 percent of antimony, the balance being substantially allaluminum, and characterized by an adaptability to acquire an excellentfinish when oxide coated.

3. An aluminum base alloy suitable for die castings, and consistingessentially of between 3.5 percent and 6.0 percent of zinc, between 0.6percent and 2.0 percent of iron, between about 0.25 percent and 2.0percent of antimony, between 0.15 percent and 0.50 percent of manganese,and between 0.15 and 0.5 percent of magnesium, the balance beingsubstantially all aluminum, and characterized by an adaptability toacquire an excellent finish when oxide coated.

4. An aluminum base alloy suitable for die castings, and consistingessentially of between 3.5 percent and 6.0 percent of zinc, between 0.6percent and 2.0 percent of iron, between about 0.25 percent and 2.0percent of antimony, between 0.15 percent and 0.50 percent of manganese,and up to 2.0 percent of silicon, the balance being substantially allaluminum, and characterized by an adaptability to acquire an excellentfinish when oxide coated.

5. An aluminum base alloy suitable for die castings, and consistingessentially of between 3.5 percent and 6.0 percent of zinc, between 0.6percent and 2.0 percent of iron, between about 0.25 percent and 2.0percent of antimony, between 0.15 percent and 0.50 percent of manganese,and between 0.1 percent and 2.0 percent of cop per, the balance beingsubstantially all aluminum, and characterized by an adaptability toacquire an excellent finish when oxide coated.

6. An aluminum base alloy suitable for die castings, and consistingessentially of between 3.5 percent and 6.0 percent of zinc, between 0.6percent and 2.0 percent of iron, between about 0.25 percent and 2.0percent of antimony, between 0.15 percent and 0.5 percent of magnesium,and up to 2.0 percent of silicon, the balance being substantially allaluminum, and characterized by an adaptability to acquire an excellentfinish when oxide coated.

7. An aluminum base alloy suitable for die castings, and consistingessentially of between 3.5 percent and 6.0 percent of zinc, between 0.6percent and 2.0 percent of iron, between about 0.25 percent and 2.0percent of antimony, between 0.15 percent and 0.50 percent of manganese,between 0.15 percent and 0.5 percent of magnesium, and between 0.1percent and 2.0 percent of copper, the balance being substantially allalluminurn.

8. An aluminum base alloy suitable for die castings, and consistingessentially of between 3.5 percent and 6.0 percent of zinc, between 0.6percent and 2.0 percent of iron, between about 0.25 percent and 2.0percent of antimony, between 0.15 percent and 0.50 percent of manganese,between 0.15 percent and 0.5 percent of magnesium, up to 2.0 percent ofsilicon, and between 0.1 percent and 2.0 percent of copper, the balancebeing substantially all aluminum.

9. An aluminum base alloy suitable for die castings, and adapted toacquire an excellent finish when oxidecoated, and consisting essentiallyof about 4.5 percent of zinc, about 0.9 percent of iron, about 0.25percent of manganese, about 1.0 percent of antimony, about 0.3 percentof magnesium, the balance being substantially of aluminum.

10. An aluminum base alloy suitable for die castings, and consistingessentially of about 4.5 percent of zinc, about 0.9 percent of iron,about 1.0 percent of antimony, and up to 2.0 percent of silicon, thebalance being substantially all aluminum, and characterized by anadaptability to acquire an excellent finish when oxide coated.

11. An aluminum base alloy suitable for die castings, and consistingessentially of about 4.5 percent of zinc, about 0.9 percent of iron,about 1.0 percent of antimony, about 0.25 percent of manganese, and upto 2.0 percent of silicon, the balance being substantially all aluminum,and characterized by an adaptability to acquire an excellent finish whenoxide coated.

12. An aluminum base alloy suitable for die castings, and adapted toacquire an excellent finish when oxidecoated, and consisting essentiallyof about 4.5 percent of zinc, about 0.9 percent of iron, about 1.0percent of antimony, about 0.25 percent of manganese, and between 0.1percent and 2.0 percent of copper, the balance being substantially allaluminum.

13. An aluminum base alloy suitable for die castings, and adapted toacquire an excellent finish when oxidecoated, and consisting essentiallyof about 4.5 percent of zinc, about 0.9 percent of iron, about 0.25percent of manganese, about 1.0 percent of antimony, between about 0.15percent and 0.5 percent of magnesium, and between about 0.1 percent and2.0 percent of copper, the balance being substantially all aluminum.

14. An aluminum base alloy suitable for die castings, and adapted toacquire an excellent finish when oxide coated, and consistingessentially of about 4.5 percent of zinc, about 0.9 percent of iron,about 0.25 percent of manganese, about 1.0 percent of antimony, betweenabout 0.15 percent and 0.5 percent of magnesium, and up to 2.0 percentof silicon, the balance being substantially of aluminum.

15. An aluminum base alloy suitable for die castings, and adapted toacquire an excellent finish when oxidecoated, and consisting essentiallyof about 4.5 percent of zinc, about 0.9 percent of iron, about 1.0percent of antimony, about 0.25 percent of manganese, between about 0.15percent and 0.5 percent of magnesium, up to 2.0 percent of silicon, andbetween about 0.1 percent and 2.0 percent of copper, the balance beingsubstantially all aluminum.

References Cited in the file of this patent FOREIGN PATENTS 819,263France July 5, 1937

1. AN ALUMINUM BASE ALOY SUITABLE FOR DIE CASTINGS, AND CONSISTINGESSENTIALLY OF BETWEEN 3.5 PERCENT AND 6.0 PERCENT OF ZINC, BETWEEN 0.LPERCENT AND 2.0 PERCENT OF IRON, AND BETWEEN 0.25 PERCENT AND 2.0PERCENT OF ANTIMONY, THE BALANCE BEING SUBSTANTIALLY ALL ALUMINUM, ANDCHARACTERIZED BY AND ADAPTABILITY TO ACQUIRE AN EXCELLENT FINISH WHENOXIDE COATED.